Clinical severity of noise in ECG

Objective noise metrics such as the signal to noise ratio and the root mean squared value, are not always related to the actual impact that noise can have on the clinical evaluation of cardiac signals. This work is intended to design a database along with a set of criteria to be used as an initial solid gold-standard of noise severity within a scale created from the clinical point of view. Different from previous approaches, we used recordings from external cardiac event recorders, which have a signal morphology and characteristics typical for the usual Holter monitoring devices. These recorded events often correspond to noise segments, which makes simpler the retrieval of a variety of signal segments with real noise examples. We generated a database recordings from 8 patients (4 female and 4 male with a clinical indication for long-term monitoring, 64.75±25.44 years old). In a first attempt, a set of rules for clinical quality recording were initially defined by a cardiologist, so segments with clear clinical description were categorized into free, low, moderate, hard, or other noise. Segments with unclear description are set apart for revision. This process was iterated until convergence of expert opinion and labels. A specific software tool was created and modified for supporting the process for each iteration. The relative duration of the different kinds of noise in both leads according to their clinical severity was: 4h 14m 15s (free, 37.32%), 2h 54m 52s (moderated, 25.67%), 2h 21m 46s (hard, 20.81%), 1h 43m 13s (low, 15.15%) and 07m 07s - other - (1.05%). The generated database and criteria represent a valuable gold standard for clinical quality evaluation of noise impact on ECG signals.